Attract monarch butterflies to your garden

Q: My daughter and I planted a butterfly garden this spring. We have had quite a few visitors to our garden, but no monarchs have been attracted. We planted butterfly bushes, lantana, verbena and many other suggested butterfly plants, but so far no luck. Is there another plant they are more attracted to?

A: Your plant selections are great nectar plants for all butterflies. Let me share a few key points about what is arguably our national butterfly, the monarch. Almost half of our population could recognize this orange and black butterfly, yet most could not name the most important plant in the monarch butterfly’s life. Quite simply, it is milkweed, a class of more than 100 varieties of leafy green plants so named for the milky sap that oozes from its stem when snapped.

A quick look at the monarch life cycle explains why. Female monarchs lay their eggs on milkweed, a member of the Asclepias genus, the only plant monarch caterpillars eat. After hatching, the caterpillars (larvae) begin eating the milkweed.

The monarch butterfly caterpillars then store toxins known as cardenolides, obtained from their milkweed diet, specifically to make themselves poisonous to birds. The adult butterfly retains those toxins. Read “The Case of the Barfing Blue Jay” on Science Friday (sciencefriday.com) to learn more.

Survival to breed and further the species is the crucial element when you are a beautiful butterfly flitting about the garden. Being unpalatable is their only weapon.

Few among the public at large are aware the monarch butterfly is in a survival struggle. Pesticides and herbicides creating loss of habitat for breeding are major contributors. In the past 20 years, the North American population of monarchs has decreased by 90 percent, down from a population of approximately 1 billion in 1996-97, to a population of approximately 33 million in 2013-14.

Most researchers feel the loss of winter habitat due to illegal logging is the biggest threat to species survival. The monarch is the only butterfly known to make a two-way migration each year. They migrate every fall and overwinter in the Sierra Madre mountains of Mexico. Unlike other butterflies that can overwinter as larvae, pupae or even as adults in some species, monarchs cannot survive the cold winters of northern climates. The 2016 count shows gains that are credited to favorable weather and a long growing and breeding season. Native milkweed habitat replacement seems the best remedy, and many groups have heard the call.

Asclepias plants are not always generally available at your local nursery or big box store. Ideal native varieties such as butterfly weed (Asclepias tuberosa) are even more scarce. While more prevalent, the non-native tropical milkweed (Asclepias curassavica) is not suggested by some scientists for home butterfly garden plants. Although monarchs love the nectar and lay eggs on it, researchers state the plant grows and blooms for too many months, allowing disease or parasites to attach that will harm the eggs and larvae or even the adult butterfly. Other sources fear the availability of tropical milkweed late in the year will entice the butterflies to stay too long in the Deep South and succumb to freezing weather. Further studies are needed before scientists can agree on these points.

Before you start digging up your tropical milkweed, though, understand that many “Save the Monarch” groups suggest cutting back your tropical milkweed plants several times each year can keep the growth fresh and lessen the chances it will become contaminated. Keeping it trimmed off in late fall will also urge monarchs to keep traveling to their winter home.

More and more garden centers are making the effort to have native Asclepias plants available. Growing native plants is always your best option.